If I was informed correctly, the Martian atmosphere is over 95% Carbon Dioxide.. Here on earth, trees are supposed to breath in carbon dioxide and breath out oxygen. If we were to send trees to mars and had robot rovers plant them (provided that water was found), do you think that these trees could produce enough oxygen to sustain life as we know it?
Other factors come into play in a plant’s life cycle: temperature, sunlight, nutrients in the soil, and how deep the soil is (anchoring the tree/plant into the ground).
The idea of terraforming Mars has been around for a long long time. I won’t go into the details, but there’s a lot more to it than just shooting up a few pine seedlings and waiting for a while. For starters, trees need soil as well as carbon dioxide, and soil is really very complex, requiring a whole thriving microbiology. Anyway, if you’re really interested, read the Mars trilogy by Kim Stanley Robinson, which, though pure sci-fi, paints a detailed and thoughtful picture of how terraforming Mars might go and a lot of the obstacles that would have to be overcome.
Obstacles such as dying of boredom halfway through reading the series? 
(I kid, I kid. Well, sortof. A lot of people like it, but I just found it rather dull.)
Actually, I had to force myself to finish it, too. But it still does a good job of portraying Martian terraforming.
Finally realized what was bugging me about my post all day. Or actually, the lack of was bugging me.
It was bugs. And birds. And other animals. And wind.
These would be needed for pollen transfer and eventual seed dispersement; as well, in some species of plants, the seeds need to travel through an animal’s digestive tract to remove a protective hard coating so the seed can sprout.
In addition, wouldn’t the lack of an ozone layer be a hindrance in keeping out radiation (or does Mars have an ozone layer - not sure)?
Mars doesn’t have any ozone layer to speak of (it might be there, but if it is, it’s so damned thin as to not matter).
There’s probably no way that Earthly plant life could survive on Mars, it’s simply too cold. However genetically engineered plants normally found growing in arctic and antarctic regions on the Earth could, in theory, survive on Mars. Since you’re tinkering around with the plants’ DNA, you could do away with any need for pollenation/seed processing by animals or insects.
IAC, even if you started the plants growing on Mars today, it’d take a thousand years at least, before Mars had anything approaching a breathable atmosphere. (Which is why, IMHO, we need to get started now.)
I seem to recall reading that most of the oxygen in our atmosphere is actually generated not by rooted plants, but by phytoplankton in the ocean. So I guess the first step is to make a big body of water somewhere on Mars, dump a bunch of plankton into it, and wait.
Well, Mars will have to get a whole lot warmer for that to happen. Even on summer days, the place is pretty cold. One of the ideas of using lichen is that the dark green color of the plant will absorb sunlight and help to warm things up. Carl Sagan had the idea of dumping the plants on the ice caps, so that they’d melt the caps and release the CO[sub]2[/sub] and water that’s thought to be frozen in them.
The difficulties with Mars right now are the thin atmosphere and the low temperatures. Increasing the atmosphere would help the temperature due to greenhouse gases helping to hold heat from the sun.
IMHO, the best proposal I’ve heard is to send spacecraft out to redirect comets into Mars. Aiming them at the icecaps would get lots of gases from there and from the comets, which are mostly methane, ammonia, carbon dioxide and water, all of which contribute to the greenhouse effect. Then as soon as the craters start to cool a bit, seed them with cyanobacteria (formerly called ‘blue-green algae’). There are species that live in all sorts of harsh conditions, and some are photosynthetic, so we start getting oxygen. As conditions get better for Earth life, we’d keep seeding with a wider variety of organisms until there’s a functioning ecology we can live in.
I recall reading about the atmosphere leaking away because of Mars’s smal size, but the author of the article estimated that it would take a million years or so - not really an emergency.
Any atmosphere that we created today would be more stabile than Mars’ early atmosphere was, because the period of heavy bombardment that likely dispersed most of it into space is over. It would still leak, but well within manageable levels. ( assuming we have the ability to manage getting an atmosphere in the first place)
To me, a combination of black lichen and comets would be the best way to go forwards with terrforming. Seems to me that the best way to use the comets is to keep hitting the same spot over and over, preferebly over one of the ice caps, to dig a hole into the mantle and let many of the gasses and heat that are lingering there due to the lack of plate tetonics out.
Red Mars awesome book, good story of what possible terriforming of Mars would be like.
Green Mars Meh…it was ok, not the best, but it still had the same vision from the first one, so it was worth the time to read.
Blue Mars…wtf? Not in the same league as the first one, and not a worthy ending.
The only possible problem with using comets that I can think of, is the number of them which are easily available to us in the inner solar system has got to be pretty low. The Oort Cloud, which is supposed to be just stocked with them is something like half a lightyear or more from Earth. Seems to me that if you can manage to send something out to the Oort Cloud and then to Mars in a relatively short period of time (say under 40 years), you’ve got the technology to migrate to another solar system where there’s a habitable planet already.
One idea which I’ve thought of, that I haven’t seen mentioned anywhere else is sort of a “two for one” deal: An idea often bandied about for warming up Mars is to construct a giant solar mirror which will focus more of the sun’s rays on Mars, thereby warming the planet up. Why not build two of those giant mirrors? Stick one around Mars to warm it up, put the other one so that it blocks light from reaching Venus. This will freeze the Venusian atmosphere solid in a short period of time. Once that’s done, robotic vehicles could mine the ice, then send it hurtling towards Mars (on paths which take the chunks above and below the plane of elliptic, thus eliminating the danger of an errant iceball hitting us). This will dump massive amounts greenhouse gasses into the Martian atmosphere, plus thin out the Venusian atmosphere (which is something like 14 times as dense as the Earth’s), when you’ve pummped enough noxious gasses into the Martian atmosphere, you can either send the extra amounts of the Venusian atmosphere into deep space, or towards the sun. Then when you’ve got it down to a “manageable” level, you remove the mirror from around Venus, the planet slowly heats back up to a much cooler temperature, you seed the atmosphere with genetically engineered plants to produce oxygen, and by the time they’re done with that, you’ll have figured out a way to decrease the Venusian day so that it’s closer to Earth’s in length.